Putting your computer into hibernation mode always seems so snappy compared to taking it back out of hibernation mode and resuming your work. Why is it so much slower to spool the system back up than to spool it down?

The Question

SuperUser reader enthrops is curious:

Hibernation is supposed to write out RAM contents to disk, and coming back from hibernation is supposed to fill back RAM with saved contents. Why is coming back from hibernation slow, e.g. system is very unresponsive in general for quite some time?

So why exactly is it such a slow process to return the computer from a hibernated state?

The Answer

SuperUser contributor wolfo9999 explains:

The main cause is disk I/O. Reading and writing to a physical disk is much slower than from RAM. When your computer resumes from disk (hibernation) it also has to power up the components which may cause some slowdown. This is highly dependent on the computer. A SSD will have almost the same resume speed from disk as from RAM. Some computers let you move the mouse around before the ram has been completely filled up again, causing low response times.

Note: Assume you have 8GB of RAM and a SSD with 400MB/s throughput. It will still take 8*1024MB/400MB/s = 20.48s. This is not the same speed as resume from RAM.

Assuming a RAM throughput of 15,000MB/s, the resume time is 0.55 seconds.

One thing his answer doesn’t touch on, which definitely plays a role in perception of time when hibernating/resuming the computer, is what you’re doing during the process. Typically, when you hibernate your computer, you initiate the hibernation and then walk away (whether it takes 20 seconds or 2 minutes doesn’t matter to you, because you’re rarely there staring at it). When you resume the computer, however, you’re sitting right there staring at it waiting to get back to work so the difference between a 30 second resume and a 1 minute resume is significant.

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